i am stuck, only have cleared out 1/2 of this level, the walkthrough i read said to look for a hole, and a tunnel to go through....cant find any hole except in one area where a transport come into this room and then this door shuts on its own, and the room radiates in red, well, this hole has no tunnel in it, please help, really stuck.

you have to go into the room below it and blast the crap out of the tower so it disables the red stuff.....then ride the loader out and there is a cave/hole on the left as it turns the corner....then just run thru the cave and dont stop to shot the little buggars that are in there...stop when you see a machine, hit the use key and let the tunneler do its job....and also the cave has many twists and turns so it may take a while....